Palladium and half sandwich ruthenium(II) complexes of selenated and tellurated benzotriazoles: Synthesis, structural aspects and catalytic applications

Article abstract of DOI:10.1016/j.jorganchem.2009.11.009

1-(Phenylselenomethyl)-1H-benzotriazole (L¹) and 1-(4-methoxyphenyltelluromethyl)-1H-benzotriazole (L²) have been synthesized by reacting 1-(chloromethyl)-1H-benzotriazole with in situ generated nucleophiles PhSe^- and ArTe^-, respectively. The complexes of L¹ and L² with Pd(II) and Ru(II)(η⁶-p-cymene) have been synthesized. Proton, carbon-13, Se-77 and/or Te-125 NMR spectra authenticate both the ligands and their complexes. The single crystal structures of L¹, L² and [RuCl(η⁶-p-cymene)(L)][PF₆] (L = L¹: 3, L = L²: 4) have been solved. The Ru-Se and Ru-Te bond lengths have been found 2.4801(11) and 2.6183(10) A?, respectively. The palladium complexes, [PdCl₂(L)] (L = L¹: 1, L = L²: 2) have been explored for Heck and Suzuki-Miyaura C-C coupling reactions. The TON values are upto 95,000. The Ru-complexes have been found promising for catalytic oxidation of alcohols (TON ～ 7.8-9.4 × 10⁴). The complexes of telluroether ligands are as efficient catalysts as those of selenoether ones and in fact better for catalytic oxidation.

Full text of DOI:10.1016/j.jorganchem.2009.11.009

Journal of Organometallic Chemistry 695 (2010) 955–962
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Palladium and half sandwich ruthenium(II) complexes of selenated and tellurated
benzotriazoles: Synthesis, structural aspects and catalytic applications
*
Dipanwita Das, Pradhumn Singh, Ajai K. Singh
Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India
a r t i c l e i n f o
a b s t r a c t
1-(Phenylselenomethyl)-1H-benzotriazole (L1) and 1-(4-methoxyphenyltelluromethyl)-1H-benzotria-
zole (L2) have been synthesized by reacting 1-(chloromethyl)-1H-benzotriazole with in situ generated
Article history:
Received 18 September 2009
Received in revised form 6 November 2009
Accepted 9 November 2009
Available online 14 November 2009
nucleophiles PhSeꢀ and ArTeꢀ, respectively. The complexes of L1 and L2 with Pd(II) and Ru(II)( 6-p-cym-
g
ene) have been synthesized. Proton, carbon-13, Se-77 and/or Te-125 NMR spectra authenticate both the
ligands and their complexes. The single crystal structures of L1, L2 and [RuCl( 6-p-cymene)(L)][PF6]
g
(L = L1: 3, L = L2: 4) have been solved. The Ru–Se and Ru–Te bond lengths have been found 2.4801(11)
and 2.6183(10) Å, respectively. The palladium complexes, [PdCl2(L)] (L = L1: 1, L = L2: 2) have been
explored for Heck and Suzuki–Miyaura C–C coupling reactions. The TON values are upto 95,000. The
Ru-complexes have been found promising for catalytic oxidation of alcohols (TON ꢁ 7.8–9.4 ꢂ 104).
The complexes of telluroether ligands are as efficient catalysts as those of selenoether ones and in fact
better for catalytic oxidation.
Keywords:
Chalcogenated benzotriazole derivatives
Palladium
Ruthenium
Crystal structure
C–C coupling reaction
Oxidation of alcohols
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
There is a current interest in half sandwich complexes of Ru(II)
having (g
6-benzene or -p-cymene) unit because some of them are
In the class of heterocyclic compounds benzotriazole deriva-
tives have an important place. In the recent past derivatives of ben-
zotriazole have been reported as chiral C-acylating reagents [1].
They show biological activities [2,3]. Solid supported benzotriaz-
oles have been used for combinatorial synthesis of amine libraries
[4]. Their potential as UV stabilizers for polymers has also been re-
ported [5]. Using benzotriazole ligands chiral bikitaite zeolite me-
tal–organic frameworks have been designed recently [6]. The
selenation and telluration of benzotriazoles can result in multiden-
tate hybrid selenium and tellurium ligands. However, among vari-
ous possible Se or Te donors having benzotriazole skeletons only
bis(1-H-benzotriazolylmethyl) selenide has been explored [7,8]
so far. It was therefore thought worthwhile to develop a high yield
synthetic route for designing L1 and L2 and explore their ligand
chemistry. In the present paper the syntheses of these ligands
and their complexes with Pd(II) and Ru(II)(p-cymene) are de-
known for their diverse catalytic activities [9,10]. Süss-Fink et al.
have carried out hydrogenation of benzene using cluster having
Ru(g
6-arene) units [11]. Arene–ruthenium complexes with salicyl-
oxazolines are suitable as asymmetric catalysts for Diels–Alder
reactions [12]. The compounds, [Ru@C@C@CR2(L)(Cl)(arene)][PF6]
(L = PCy3, PPri3), are reported as excellent catalyst precursors for
ring closing olefin metathesis by Dixneuf’s group [13]. The atom
transfer radical polymerization of methyl methacrylate has been
catalyzed with [RuCl2(
co-workers have reported that in situ generated catalyst, from
[RuCl2(
6-p-cymene)]2 and a pyrimidinium or benzimidazolium
g
6-p-cymene)(PCy3)] [14]. Dixneuf and his
g
salt in the presence of Cs2CO3, selectively promotes the diarylation
of 2-pyridylbenzene with arylbromides [15]. Acetate-assisted C–H
activation of 2-substituted pyridines with [RuCl2(g
6-p-cymene)]2
has been reported by Davies and co-workers [16]. A variety of neu-
tral ruthenium–carbene complexes, [RuCl2(carbene)(arene)] have
been used in the catalytic synthesis of furans [17]. Kharasch
additions is catalyzed with [RuCl2(g6-p-cymene)(PAr3)] [18].
Demonceau et al. have recently reported the exceptional efficacy
of [RuCl2(g6-p-cymene)(PR3)] complexes as a catalyst precursor
for the ring-opening metathesis polymerization of low-strain
scribed. The structures of L1, L2, [RuCl(
g
6-p-cymene)(L1)][PF6]
and [RuCl(
g
6-p-cymene)(L2)][PF6] have been authenticated by sin-
gle crystal X-ray crystallographic analyses. The complexes
[PdCl2(L)] (where L = L1: 1, L = L2: 2) have been found promising
for Heck and Suzuki–Miyaura C–C coupling reactions and these re-
sults are part of the present paper.
cyclo-olefins [19]. Chiral cationic (g
6-arene)(pyridylamino)ruthe-
nium(II)-complexes act as enantioselective catalysts for the
Diels–Alder reactions with good exo:endo selectivity [20]. The half
sandwich compounds of Ru(II) show promising anticancer activity
[21–25]. Thiolate ligand oxygenation is believed to activate
* Corresponding author. Tel.: +91 11 26591379; fax: +91 11 26581102.
E-mail addresses: ajai57@hotmail.com, aksingh@chemistry.iitd.ac.in (A.K.
Singh).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.009

956
D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
cytotoxic half sandwich [Ru(
g
6-arene)(en)(SR)]+ complexes to-
2.1. Synthesis of L1
ward DNA binding [26]. Ru(II)–arene complexes with pyrone-de-
rived ligands are rendered active against cancer cells by
replacement of the coordinated (O,O) donor with (S,O) donor
[27]. Hartinger and co-workers [28] have reported that promising
cytotoxic effects of water-soluble dinuclear Ru–arene complexes
in human cancer cells can be increased by increasing the spacer
Diphenyldiselenide (0.32 g, 1 mmol) dissolved in 30 mL of EtOH
was stirred under nitrogen atmosphere and treated with a solution
of sodium borohydride (0.076 g, ꢁ2 mmol) made in 5 mL of aque-
ous NaOH (5%) dropwise till it became colourless due to the forma-
tion of PhSeNa. 1-(Chloromethyl)-1H-benzotriazole (0.34 g,
2 mmol) dissolved in 10 mL of ethanol was added to the colourless
solution with constant stirring and the mixture stirred further for
3 h. It was poured into cold water (30 mL). The L1 was extracted
with chloroform (4 ꢂ 25 mL). The extract was washed with water
(3 ꢂ 40 mL) and dried over anhydrous sodium sulfate. The solvent
was evaporated off under reduced pressure on a rotary evaporator
to get a pale yellow solid. The solid on recrystallization from chlo-
roform–hexane mixture (1:1), gave pale yellow coloured single
crystals of L1. Yield 0.46 g (ꢁ80%). Anal. Calc. for C13H11N3Se: C,
54.19; H, 3.85; N, 14.58. Found: C, 53.96; H, 3.82; N, 14.46%.
NMR (1H, CDCl3, 25 °C vs. TMS): (d, ppm): 6.02 (s, 2H, H5),
7.20ꢀ7.44 (m, 8H, H1, H2, H3, H7, H8, H9), 8.02 (d, 1H, 3J = 8.1 Hz,
H10); (13C{1H}, CDCl3, 25 °C vs. TMS): (d, ppm): 43.1 (C5), 110.0
(C10), 120.0 (C7), 124.1 (C9), 127.3 (C1), 127.4 (C4), 128.8 (C8),
129.3 (C2), 132.1 (C6), 135.2 (C3), 146.3 (C11); (77Se {1H}, CDCl3,
25 °C vs. Me2Se): (d, ppm) 406.3. IR (KBr, cmꢀ1): 3732, 3004,
1435, 1219, 1064, 740, 680, 605.
length between the metal centers. The interaction of [RuCl2(g6
-
p-cymene)(pta)] reported as an effective anticancer and antimeta-
static agent, with biological nucleophiles important with respect to
its mechanism of action has been studied [29]. Organometallic
ruthenium(II)–arene complexes coordinated to maltol-derived
ligands were prepared and their anticancer activity against human
tumor cell lines was studied. [30]. Therrien and co-workers have
found that water-soluble arene ruthenium complexes containing
pyridinethiolato ligands show cytotoxicity towards ovarian cancer
cells [31]. In vitro studies by Dyson and co-workers have revealed
that (3,5,6-bicyclophosphite-a-D-glucofuranoside)(g
6-p-cymene)-
dihalogenido-ruthenium(II) complex is the most cytotoxic com-
pound for human cancer cell lines [32].
N
N
N
N
N
N
5
3
2
5
3
2
11
11
1
10
9
10
9
6
Te 4
OMe
6
Se
1
4
2.2. Synthesis of L2
7
7
L2
8
8
L1
Bis(4-methoxyphenyl)ditelluride (0.469 g, 1 mmol) was treated
with sodium borohydride (0.076 g, ꢁ2 mmol) and 1-(chloro-
methyl)-1H-benzotriazole (0.34 g, 2 mmol) as described in Section
2.1 for diphenyldiselenide. The L2 was isolated by a workup de-
scribed for L1 and its single crystals were also obtained by a similar
procedure. Yield 0.580 g (ꢁ80%). Anal. Calc. for C14H13N3OTe: C,
45.83; H, 3.57; N, 11.45. Found: C, 45.77; H, 3.39; N, 11.38%.
NMR (1H, CDCl 3, 25 °C vs. TMS): (d, ppm): 3.78 (s, 3H, OMe),
6.11 (s, 2H, H5), 6.68 (d, 3J = 9 Hz, 2H, H2), 7.22 (t, 3J = 8.0 Hz, 1H,
H8), 7.38 (m, 2H, H7 + H9), 7.54 (d, 3J = 8.4 Hz, 2H, H3), 8.03 (d,
3J = 8.1 Hz, 1H, H10); (13C{1H} CDCl 3, 25 °C vs. TMS): (d, ppm):
21.0 (C5), 55.2 (OCH3), 100.7 (C4), 110.7 (C10), 115.4 (C2), 120.1
(C7), 124.0 (C9), 127.0 (C8), 132.2 (C6), 142.7 (C3), 146.3 (C11),
160.7 (C1); (125Te {1H}, CDCl3, 25 °C vs. Me2Te) (d, ppm), 705.4. IR
(KBr, cmꢀ1): 3007, 2947, 1484, 1239, 1058, 748, 514, 262.
The half sandwich species [RuCl(
g
6-p-cymene)(L)][PF6] (L = L1:
3, L = L2: 4) have been found promising for catalytic oxidation of
primary alcohols with N-methylmorpholine-N-oxide (NMO). These
results are also given in the present paper.
2. Experimental
The C and H analyses were carried out with a Perkin–Elmer
2400 Series II C, H, N analyzer. The 1H, 13C{1H}, 77Se{1H} and
125Te{1H}NMR spectra were recorded on a Bruker Spectrospin
DPX-300 NMR spectrometer at 300.13, 75.47, 57.24 and
94.69 MHz, respectively. IR spectra in the range 4000–250 cmꢀ1
were recorded on a Nicolet Protége 460 FT-IR spectrometer as
KBr pellets. Single crystal X-ray diffraction data for L1, L2 and
2.3. Synthesis of [PdCl2(L1)] (1) and [PdCl2(L2)] (2)
[RuCl(
with a Bruker AXS SMART Apex CCD diffractometer using Mo K
g
6-p-cymene)(L)][PF6] (L = L1: 3, L = L2: 4) were collected
a
The solution (in 5 mL water) of Na2[PdCl4] (0.294 g, 1 mmol)
was mixed with a solution of L1 (0.288 g, 1 mmol) or L2 (0.367 g,
1 mmol) made in acetone (10 mL) with vigorous stirring. An orange
precipitate of 1 or 2 obtained instantaneously. The precipitate was
filtered, washed with water and dried.
1: Yield ca. 0.368 g (ꢁ79%). Anal. Calc. for C13H11Cl2N3PdSe: C,
33.55; H, 2.38; N, 9.03. Found: C, 33.60; H, 2.09; N 9.13%. NMR
(1H, DMSO-d6, 25 °C vs. TMS): (d, ppm) 6.37 (s, 2H, CH2),
7.18ꢀ7.28 (m, 3H, H1 + H2), 7.37ꢀ7.44 (m, 3H, H3, H8), 7.52 (t,
3J = 9 Hz, 1H, H9), 7.76 (d, 3J = 8.7 Hz 1H, H7), 8.00 (d, 3J = 9 Hz,
1H, H10); (13C{1H}, DMSO-d6, 25 °C vs. TMS): (d, ppm) 44.4 (C5),
112.5 (C10), 119.2 (C7), 124.4 (C9), 127.1 (C1), 128.2 (C4), 128.9
(C8), 129.4 (C2), 133.7 (C6), 134.4 (C3), 145.4 (C11); (77Se{1H}
DMSO-d6, 25 °C vs. Me2Se): (d, ppm) 420.6. IR (KBr, cmꢀ1): 3488,
3022, 1448, 1309, 1226, 744, 305.
2:. Yield ꢁ 0.480 g (ꢁ90%). Anal. Calc. for C14H13Cl2N3OTePd: C,
30.90; H, 2.41; N, 7.72. Found: C, 29.53; H, 2.42; N, 5.81%. NMR (1H,
DMSO-d6, 25 °C vs. TMS) (d, ppm) 3.78 (s, 3H, OMe), 6.75 (s, 2H,
H5), 6.90 (d, 3J = 9 Hz, 2H, H2), 7.37 (t, 3J = 9 Hz, 1H, H8), 7.54 (t,
3J = 9 Hz, 1H, H9), 7.56 (d, 3J = 8.7 Hz, 2H, H3), 7.71 (m, 1H, H7),
7.95 (d, 3J = 9 Hz, 1H, H10); (13C{1H} DMSO-d6, 25 °C vs. TMS): (d,
(0.71073 Å) radiations at 298 (2) K. The SHELXTL was used for space
group, structure determination and refinements [33,34]. For
absorption correction (if needed) software SADABS was used [35].
Hydrogen atoms were included in idealized positions with isotro-
pic thermal parameters set at 1.2 times that of the carbon atom
to which they were attached. In Table S.1 of online Supplementary
material crystal data and structural refinements are summarized.
The catalytic oxidation yields were determined with NUCON Engi-
neers (New Delhi, India) gas chromatograph (with FID detector),
model 5765 equipped with an Alltech (EcTM-1) column of 30 m
length, 0.25 mm diameter and having liquid film of 0.25 lm thick-
ness. The cyclic voltammetric studies were performed on BAS CV
50 W instrument at University of Delhi (Department of Chemistry),
India. A three-electrode configuration composed of Pt disk working
electrode (3.1 mm2 area), Pt wire counter electrode and Ag/AgCl
reference electrode was used for the measurements. Ferrocene
was used as an internal standard (E1/2 = 0.500 V vs. Ag/AgCl) and
all the potentials are expressed with reference to Ag/AgCl. The
[{RuCl(
ture method [36].
l-Cl)(g
6-p-cymene)}2], were prepared according to litera-

D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
957
ppm) 34.3 (C5), 55.2 (OCH3), 106.2 (C4), 110.9 (C10), 115.0 (C2),
119.2 (C7), 124.9 (C9), 127.5 (C8), 132.6 (C6), 138.4 (C3), 145.1
(C11), 161.1 (C1); (125Te{1H}, DMSO-d6, 25 °C vs. Me2Te): (d, ppm)
722.4. IR(KBr, cmꢀ1): 3454, 2953, 1580, 1489, 1251, 1177, 748, 325.
anhydrous Na2SO4 and the solvent was evaporated on a rotary
evaporator to obtain the product which was purified by flash
chromatography.
2.7. Procedure for catalytic oxidation of alcohols
2.4. Synthesis of [RuCl(g g
6-p-cymene)(L1)][PF6] (3) and [RuCl( 6-p-
cymene)(L2)][PF6] (4)
A typical procedure used for catalytic oxidation of primary alco-
hols to corresponding aldehydes and secondary alcohols to ketones
with N-methylmorpholine-N-oxide (NMO) and complexes 3 or 4 is
as follows. A solution of ruthenium complexes (0.001 mol%) in
20 cm3 of CH2Cl2 was added to the solution of substrate (1 mmol)
and NMO (3 mmol) made in CH2Cl2. The mixture was refluxed for
3 h and solvent was evaporated off under reduced pressure. The
resulting reaction mixture containing the complex 3 or 4 and the
oxidized product was extracted with petroleum ether (60–80 °C)
(20 cm3). The complex 3 or 4 precipitated as solid was recovered
quantitatively for next catalytic cycle. The oxidized product sepa-
rated in petroleum ether was analyzed by GC.
[Ru(g6p-cymene)Cl2]2 (0.061 g, 0.1 mmol) dissolved in 10 mL of
dry methanol was treated with L1 (0.288 g, 0.1 mmol) or L2
(0.367 g, 0.1 mmol) dissolved in 10 mL of dry methanol with vigor-
ous stirring. The reaction mixture was stirred further overnight. Its
volume was reduced to ꢁ5 mL on a rotary evaporator and ammo-
nium hexafluorophosphate (0.0163 g, 0.1 mmol) was added to get
an orange precipitate of 3 or 4. The precipitate was filtered and
washed with cold methanol. The single crystals of 3 and 4 both
were grown from chloroform and acetonitrile mixture (1:1).
3: Yield ꢁ 0.035 g (ꢁ50%); Anal. Calc. for C23H25ClN3SeRuPF6: C,
39.25; H, 3.58; N, 5.97. Found: C, 39.53; H, 3.42; N, 5.81%. NMR:
(1H, CDCl3, 25 °C vs. TMS) (d, ppm): 1.28ꢀ1.32 (m, 6H, CH3 of i-
Pr), 2.00 (s, 3H, CH3 of p-cymene, p to i-Pr), 2.73ꢀ2.85 (m, 1H,
CH of i-Pr), 5.44ꢀ5.67 (m, 4H, Ar–H of p-cymene), 5.94 (s, 2H,
H5), 7.18ꢀ7.63 (m, 6H, H1 + H2 + H8 + H9 + H7), 7.70ꢀ7.71 (m, 2H,
H3), 8.17 (d, 3J = 8.4 Hz, 1H, H10. The stability of solution of 3 for
recording carbon-13 NMR was inadequate. (77Se{1H}, CDCl3, 25 °C
vs. Me2Se): (d, ppm) 401.4. IR (KBr, cmꢀ1): 3450, 2950, 1584,
1490, 1243, 1137, 840, 738, 320.
3. Results and discussion
The ligands L1 and L2 and their complexes have been synthe-
sized by the reactions given in Scheme 1. The ligands are non-elec-
trolytes and stable as they can be stored under ambient conditions
up to 6 months. In CHCl3, CH2Cl2, CH3CN, CH3OH, C2H5OH and ace-
tone their solubility is good but poor in hexane. The complexes 1
and 2 are soluble in DMSO and almost insoluble in CHCl3, CH2Cl2,
CH3CN, EtOH, MeOH, acetone and hexane. However, their solutions
in DMSO on keeping for more than 12 h or exposing them to air
show the sign of decomposition. The complexes 3 and 4 expected
to be chiral have been isolated as racemic mixture. They are stable
under ambient conditions and soluble in CHCl3, CH2Cl2, CH3CN,
EtOH, MeOH and acetone but almost insoluble in hexane. The solu-
tions of 3 and 4 in DMSO also show the signs of decomposition
after 5–6 h.
The cyclic voltammetric (CV) experiments performed at 298 K
in CH3CN (0.01 M N(n-Bu)4ClO4 as supporting electrolyte) for both
3 and 4 at scan rate 100 mV sꢀ1 (anodic sweep) show two metal
centered voltammetric responses. A quasi-reversible oxidation
(Fig. S.1) with E1/2 values +0.588 and +0.644 V (vs. Ag/AgCl),
respectively, for 3 and 4 has been observed. More details are in Ta-
ble S.3 of online Supplementary material. The higher value of E1/2
for 4 in comparison to that of 3 suggests that substitution of (N,
Se) ligand with a (N, Te) at ruthenium center leads to a less ther-
modynamically favourable oxidation. Moreover these E1/2 values
indicate that 3 and 4 are expected to be reasonably efficient cata-
lyst for a redox process [37].
4: Yield ꢁ 0.046 g (ꢁ60%); Anal. Calc. for C24H27ClN3OTeRuPF6:
C, 36.85; H, 3.48; N, 5.37. Found: C, 36.53; H, 3.42; N, 5.81%.
NMR: (1H, CDCl3, 25 °C vs. TMS): (d, ppm) 1.21ꢀ1.27 (m, 6H, CH3
of i-Pr), 1.96 (s, 3H, CH3 of p-cymene, p to i-Pr), 2.74ꢀ2.83 (m,
1H, CH of i-Pr), 3.73 (s, 3H, OCH3), 5.25 (d, 3J = 11.4 Hz, 1H, Ar–H
of p-cymene), 5.41 (d, 3J = 11.1, 1H, Ar–H of p-cymene), 5.66 (d,
3J = 6.0 Hz, 1H, Ar–H of p-cymene), 6.01ꢀ6.04 (m, 2H, H5), 6.13
(d, 3J = 6.3 Hz, 1H, Ar–H of p-cymene), 6.79 (d, 3J = 8.7 Hz, 2H,
H2), 7.14 (d, 3J = 8.4 Hz, 2H, H3), 7.52ꢀ7.70 (m, 3H, H7 + H8 + H9),
8.11 (d, 3J = 8.4 Hz, 1H, H10); (13C{1H}, CDCl3, 25 °C vs. TMS): (d,
ppm)18.8 (p-cymene CH3, p to i-Pr), 21.5, 23.0 (CH3 of i-Pr of p-
cymene), 31.8(CH of i-Pr of p-cymene), 32.1(C5), 56.2 (OCH3),
83.6, 85.1, 91.1, 92.2 (ArC of p-cymene m and o to i-Pr), 102.2
(C4), 108.1, 110.3 (ArC attached to CH3 of p-cymene + ArC attached
to i-Pr of p-cymene), 112.4 (C10), 117.0 (C2), 120.3 (C7), 127.8 &
131.4 (C9 and C8), 135.2 (C6), 138.3 (C3), 148.3 (C11), 163.2 (C1);
(
125Te{1H}, CDCl3, 25 °C vs. Me2Te): (d, ppm) 700.5. IR(KBr, cmꢀ1):
3474, 2973, 1560, 1488, 1236, 1147, 835, 740, 319.
2.5. Procedure for catalytic Heck reaction
A
mixture of methyl acrylate (1.5 mmol), aryl bromide
(1 mmol), n-butylamine (0.146 g, 2.0 mmol), p-xylene (ꢁ3 mL)
and complex 1 or 2 [10ꢀ4 M, 100
stirred for 24 h at 100ꢀ110 °C on an oil bath. It was cooled to room
temperature, treated with chloroform (40 mL) and filtered. The
chloroform extract was washed with acidified (HCl) water, dried
over anhydrous Na2SO4 and its solvent was evaporated on a rotary
evaporator to obtain the product, which further was purified by
flash chromatography.
3.1. NMR spectra
lL (in DMA), ꢁ0.001 mol%] was
The lone signal in 77Se{1H}NMR spectrum of L1 is at lower fre-
quency (56.3 ppm) with respect to that of precursor diphenyldisel-
enide, which shows a signal at 462.6 ppm. On contrary signal in
125Te{1H}NMR spectrum of L2 is at high frequency (ꢁ249 ppm) with
respect to that of precursor ditelluride whose signal appears at
456.3 ppm. The 13C{1H} and 1H NMR spectra of both L1 and L2 were
found as expected. The signal of C4 (bonded to Se) in carbon-13
spectrum of L1 appears at lower frequency (ꢁ3 ppm) with respect
to that of precursor Ph2Se2 (130.5 ppm). But the signal of C4 (bonded
to Te) in the spectrum of L2 has been observed at higher frequency
(ꢁ3 ppm) with respect to that of precursor Ar2Te2 (96.6 ppm). How-
ever, the signal of C5 appears at lower frequency (ꢁ10 ppm for L1
and ꢁ32 ppm for L2) in 13C{1H}spectra of both L1 and L2 with respect
to that of corresponding precursor chloro compound (53.5 ppm). In
1H NMR spectra of both L1 and L2 the signals of H5 protons were
2.6. Procedure for catalytic Suzuki–Miyaura reaction
A mixture of phenylboronic acid (1.5 mmol), aryl bromide
(1 mmol), K2CO3 (3 mmol), toluene (ꢁ10 mL) and complex 1 or 2
[10ꢀ4 M, 100
l
L (in DMA), ꢁ0.001 mol%] was stirred for 15 h at
100ꢀ110 °C on an oil bath. It was cooled to room temperature,
treated with chloroform (40 mL) and filtered. The chloroform
extract was washed with acidified (HCl) water, dried over

958
D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
(4-MeOC H ) Te
Ph2Se2
/
6
4 2
2
NaBH4
Aq. NaOH
N2
4-MeOC6H4TeNa
2PhSeNa
N
N
N
in dry EtOH
N2
Cl
N
N
N
N
N
N
5
3
2
5
3
2
11
11
10
6
Te
6
Se
OMe
1
1
4
4
7
9
7
9
8
8
L1
L2
Na2PdCl4
[RuCl2(p-cymene)]2
Methanol
Acetone / Water (1:1)
[RuCl(p-cymene)(L)][PF6]
[PdCl2(L)]
where L = L1 : 3
where L = L1 : 1
L = L2 : 2
L = L2 : 4
Scheme 1.
found at lower frequency (0.31ꢀ0.56 ppm) with respect to that of
along with selected bond lengths and angles. All crystal data and
precursor chloro compound (6.42 ppm) and satellites due to cou-
refinement parameters are given in online Supplementary material
0
2
pling of H5 with Se or Te (2JSe,H = 9.0 Hz; JTe,H = 18.9 Hz) observed.
(Table S.1). The Se–C(aryl) bond distance [1.916(4) ÅA] is somewhat
0
Palladium complexes 1 and 2, [PdCl2(L)] (L = L1: 1, L = L2: 2) show
77Se{1H}/125Te{1H}/NMR spectra which support their formation.
The signal in 77Se{1H} NMR spectrum of 1 is at higher frequency
with respect to that of corresponding ligand by 14 ppm. Similarly
in 125Te{1H}NMR spectra of 2 the signal appears shifted to a higher
frequency by 43.1 ppm (with respect to that of corresponding free
ligand). These high frequency shifts indicate the formation of me-
tal–chalcogen bond in the Pd-complexes 1 and 2. This is further sup-
ported by their 13C{1H} NMR spectra as signals of C5 and C4 appear at
higher frequency (C5: 1.27 (1) and 13.25 (2) ppm; C4: 0.79 (1) and
5.53 (2) ppm) with respect to those of corresponding free ligands.
The signals of H5 and H3 are also observed at higher frequency (upto
ꢁ0.6 ppm) with respect to those of corresponding free ligands in 1H
NMR spectra of 1 and 2, further supporting the formation of metal–
chalcogen bond. The single crystal structures of complexes 3 and 4
reveal the formation of metal–chalcogen bond. However, the signals
in 77Se{1H} NMR spectrum of 3 and 125Te{1H}NMR spectrum of 4 ap-
pear unexpectedly at lower frequency (ꢁ5 ppm) with respect to
those of corresponding free ligands. In 13C{1H} NMR spectrum of 4
signals of C5 as well as C4 were observed at higher frequency (C5:
11.06 ppm and C4: 1.51 ppm) with respect to those of free L2. The
signals of H3 in 1H NMR spectrum of 3 were also found at higher
frequency (0.38 ppm) with respect to those of corresponding free
ligand. Thus formation of Ru–chalcogen bond in the complexes 3
and 4 is supported by their 1H and 13C{1H} spectra.
shorter than Se–C(alkyl) distance [1.953(4) ÅA] in0 L1. Similarly in the
case of L2 Te–C(aryl) bond distance 0[2.117(3) ÅA] is found shorter
than Te–C(alkyl) distance [2.159(3) ÅA]. The bond angles C(alkyl)–
Se–C(aryl) (97.39(15)°) in L1 and C(alkyl)–Te–C(aryl) (95.16(10)°)
in L2 are as expected. The Table S.2 of online Supplementary mate-
rial has more values of bond lengths and angles. The hydrogen
atoms of CH2 group of L1 are engaged in non-covalent interaction
[Nꢃ ꢃ ꢃH hydrogen bonding (inter and intra molecular both)] which
may be the result of stacking forces. The p–p interactions between
the benzotriazole rings are also present in its crystal, probably due
to similar reason. In case of L2 also both intermolecular Nꢃ ꢃ ꢃH and
Oꢃ ꢃ ꢃH non-covalent interactions (hydrogen bonding) probably due
to stacking have been observed. Further details of these non-cova-
C4
C3
C11
C5
C6
C10
C8
C2
C9
C12
C13
C1
N1
N3
N2
C7
Se1
3.2. Crystal structures
0
Fig. 1. ORTEP diagram of L1 with 30% probability ellipsoids: bond distances (AÅ):
Se(1)–C(8) 1.916(4), Se(1)–C(7) 1.953(4), N(3)–C(6) 1.366(5); bond angles (°): C(8)–
Se(1)–C(7) 97.39(15), N(1)–C(7)–Se(1) 114.5(2), N(3)–N(2)–N(1) 109.1(3).
The crystal structures of L1, L2, 3 and 4 have been solved. Molec-
ular structures of L1 and L2 are shown in Figs. 1 and 2, respectively,

D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
959
C5
C4
C6
N1
N2
C3
C2
C13
C12
C1
O1
N3
C7
C11
C8
C14
Te1
C10
C9
0
Fig. 2. ORTEP diagram of L2 with 30% probability ellipsoids: bond distances (AÅ):
Te(1)–C(7) 2.159(3), Te(1)–C(8) 2.117(3), N(3)–C(7) 1.447(3); bond angles (°):
N(1)–N(2)–N(3) 109.0(2), C(7)–Te(1)–C(8) 95.16(10), Te(1)–C(7)–N(3) 115.69(17).
lent interactions are given in online Supplementary material
(Figs. S.3–S.5).
Fig. 4. ORTEP diagram of cation of 4 with 30% probability ellipsoids; bond distances
0
The ORTEP diagrams of cation of 3 and 4 are given in Figs. 3 and
4, respectively, with their some selected bond lengths and angles.
Further details are given in the online Supplementary material
(Table S.2). In both the cations of 3 and 4, Ru exhibits the pseu-
do-octahedral half sandwich ‘‘piano-stool” disposition around Ru.
The ring of p-cymene occupies one face of octahedron. The Ru-
complexes of selenoether ligands have scantly investigated. How-
(AÅ): Te(1)–Ru(1) 2.6183(10), Ru(1)–N(2) 2.085(7), Ru(1)–Cl(1) 2.412(3), Ru(1)–C
2.170(10)–2.231(10); bond angle (°): N(2)–Ru(1)–Cl(1) 87.6(2), N(2)–Ru(1)–Te(1)
82.6(2), Cl(1)–Ru(1)–Te(1) 79.88(8).
ters [Ru3(
S)(CO)7(
-dppm)] [41]. For Ru(IV) complex [RuCp*{
Pr)2{
2-SeP(i-Pr)2}][PF6] the Ru–Se bond lengths [42] are reported
l
3-Se)(CO)7(
l
3-CO)(
l
-dppm)] and [Ru3(
l
g
3-Se)(l3
-
l
2-Se2P(i-
ever, Ru(II)(g g
6-benzene)- and Ru(II)( 6-p-cymene)-complexes of
g
selenated pyrrolidine derivatives have been reported by our
research group recently in which Ru is coordinated through Se
and N forming a five membered chelate ring [38]. The 3 is another
example of such Ru–selenoether complex. The Ru–C distances
(2.182(7)–2.225(8) Å) in the cation of 3 are normal and consistent
in the range 2.538(2)–2.590(2) Å, longer than that of cation of 3
due to steric crowding. The Ru–Se bond distance found in bimetal-
lic species [RuCp(CO)(C„CPh)(
closer to that of cation of 3. In [Ru(
5-C5Me5)]Cl (R = Tolyl) Ru–Se bond distances are in the range
l
-Se)ZrCp2] 2.494(1) Å [43], is
g
5-C5Me5)(
l2-SeR)3Ru-
(g
with the earlier reports [38–40]. In the crystal of 3,
p–p and
2.446(4)–2.466(4) Å [44] and shorter than that of cation of 3,
C–Hꢃ ꢃ ꢃ
p
interactions along with intra and inter molecular non-
because RSeꢀ is expected to be bonded strongly in comparison to
covalent interactions (hydrogen bonds) between F and various H
atoms have been observed resulting in extended structures (Figs.
S.6 and S.7 in online Supplementary material). The Ru–N bond
length in the cation of 3, 2.089(6) Å is comparable to that of cat-
a
selenoether. In
a diselenide bridged complex [Ru(MeCp)-
(PPh3)]2( -Se2)2(Otf)2, Ru–Se bond distances are 2.518(1) and
l
2.556(1) Å [45], somewhat longer than that of cation of 3. In cation
of complex 4, ligand L2 is coordinated with Ru in a bidentate (Te, N)
mode forming a five membered chelate ring. The Ru–N bond length
(2.085(7) Å) is consistent with the sum of covalent radii ca. 1.95 Å
ion of
4
and consistent with recent literature reports
(2.0511(17)–2.163(10) Å) [39,40]. It is however, shorter than
2.146(3)–2.201(5) Å reported for half sandwich complex of Ru(II)
with N-{2-(phenylseleno)ethyl}pyrrolidine [38]. The Ru–Se bond
length of the cation of 3 (2.4801(11) Å) falls within the range
2.4756(10)–2.5240(9) Å reported for Ru–Se bond lengths in clus-
and with literature reports of 2.142(3) Å for [{RuCl(g
6-p-cyme-
ne)(H2NCH2CH2Te-C6H4OMe)}ClꢃH2O] [46], 2.141(2)ꢀ2.156(2) Å
for
[RuCl(
g
6-p-cymene)(o-phenylenediamine)][PF6]
[47],
6-benzene)-complexes of
6-p-cymene)-complexes of
2.0652(19)ꢀ2.0756(19) Å for Ru(II)(
g
g
bis(pyrazol-1-yl)pyridazine and Ru(II)(
3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine [48], 2.13(1)ꢀ2.14(1) Å
for [RuCl(
6-p-cymene)( 2-N,O-phenylalanineamide)] [49], 2.060(5)
and 2.079(4) Å for [RuCl(
6-p-cymene){2,3-bis(2-pyridyl)pyra-
6-p-cymene)-
C22
g
j
g
C12
C8
C21
zine}]ꢃBF4 [50] and 2.077(3)ꢀ2.113(3) Å for Ru(II)(
g
C23
Se1
C17
complexes of oxazoline-based ligands [51]. The Ru–Te bond length
C11
C10
C7
(2.6183(10) Å) of cation of 4 is consistent with earlier reports
Cl1
2.619(8) Å for [RuCl2(g
6-p-cymene)L] where L is 2-(4-ethoxy-
C18
phenyl telluromethyl)tetrahydro-2H-pyran [52] and 2.6371(4) Å
C13
Ru1
C16
for [{RuCl(
g
6-p-cymene)(H2NCH2CH2TeC6H4OMe)ClꢃH2O] [46]. It
C19
C20
C9
N2
is somewhat shorter than 2.6528(9) Å for [dichloro(g
6-p-cymene)-
C15
C14
C6
bis{2-(2-thienyl)ethyl}telluride]ruthenium(II) [53], 2.651(5) Å for
N3
[RuCl2(
g
6-p-cymene){bis(1,3-dioxan-2-yl)}ethyl telluride}] [54]
0
C5
C4
and 2.6559(9) ÅA for [RuCl2(
nyltelluro)ethyl]-phthalimide}] [55]. The hybrid organotellurium
ligands in all these complexes of Ru(II)(
6-p-cymene) bind in a
g
6-p-cymene){N-[2-(4-methoxyphe-
N1
C1
C2
g
monodentate mode via Te and probably this may be responsible
C3
to some extent for the longer Ru–Te bond lengths observed in
0
them. The Ru–Cl bond length of the cation of 4, 2.412(3) ÅA (sum
Fig. 3. ORTEP diagram of cation of 3 with 30% probability ellipsoids; bond distances
0
of covalent radii ca. 2.24 Å) is consistent with earlier reports
0
(AÅ): Ru(1)–N(2) 2.089(6), Ru(1)–Cl(1) 2.416(2), Ru(1)–Se(1) 2.4801(11), Ru(1)–C
2.182(7)–2.225(8); bond angle (°): N(2)–Ru(1)–Cl(1) 86.92(18), N(2)–Ru(1)–Se(1)
81.41(17), Cl(1)–Ru(1)–Se(1) 80.49(6).
2.415(2)/2.422(2) ÅA for [dichloro(
g
6-p-cymene)bis{2-(2-thienyl)-
0
ethyl}telluride]ruthenium(II) [36],
2.417(2)ꢀ2.436(2) ÅA for

960
D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
Table 1
Table 2
Parameters for catalytic performance of 1 and 2 in Heck reactions of aryl halide with
Parameters of catalytic performance of 1 and 2 in Suzuki–Miyaura reactions of aryl
methyl acrylate.
bromide with phenylboronic acid.
Ar–X
1
2
Ar–X
1
2
% Con- TON
version
TOF
% Con- TON
version
TOF
(hꢀ1
% Con- TON
version
TOF
(hꢀ1
% Con- TON
version
TOF
(hꢀ1
(hꢀ1
)
)
)
)
55
28
90
92
91
55,000 2291 57
28,000 1166 30
90,000 3750 92
92,000 3833 94
91,000 3791 95
57,000 2375
30,000 1250
92,000 3833
94,000 3916
95,000 3958
40
23
85
89
91
40,000 2666 41
23,000 1533 24
85,000 5666 87
89,000 5933 92
91,000 6066 90
41,000 2733
24,000 1600
87,000 5800
92,000 6133
90,000 6000
Br
Br
Me
Me
Br
Br
Br
Br
NC
NC
OHC
O2N
OHC
O2N
Br
Br
Br
Br
[RuCl2(p-cymene)L] (L = monodentate Te-ligand) [56–58] and
[RuCl{
2-C,N-C6H3(CH2NMe2)2-2,6}{ 6-C10H14}] [59]. However,
Table 3
g
g
Catalytic oxidation of alcohols to corresponding aldehydes and ketones with
Ru–Cl bond distance of the cation of 4 is somewhat longer than
2.308(2) Å reported for [{Ru(p-cymene)Cl(H2NCH2CH2TeC6H4O-
Me)}ClꢃH2O] [46]. The Ru–C bond distances 2.170(10)ꢀ2.231(10) Å
and C–Ru–C bond angles of the cation of 4 are consistent with
earlier reports on species having Ru(p-cymene) unit [52–58]. The
bond angles at the coordinating Te and N atoms are as expected
for nearly trigonal–pyramidal and tetrahedral geometries, respec-
tively. There are non-covalent interactions (Fꢃ ꢃ ꢃH) in the crystal
of 4 (for details see online Supplementary material Fig. S.6) proba-
bly due to stacking forces.
complexes 3 and 4 in the presence of NMO.
Substrate
Product
TON (% conversion)
3
4
CHO
O
OH
1
7.8 ꢂ 104 (78) 8.2 ꢂ 104 (82)
OH
2
3
8.4 ꢂ 104 (84) 8.7 ꢂ 104 (87)
8.5 ꢂ 104 (85) 8.9 ꢂ 104 (89)
3.3. Catalytic C–C coupling and oxidation of alcohols
OH
OH
O
O
The strong donating properties of organoselenides has made
Pd(II) complex of (Se, C, Se) pincer ligand an outstanding catalyst
system [60] for Heck C–C coupling. This has motivated us to ex-
plore 1 and 2 as catalyst for Heck reaction at concentration
0.001 mol% using n-butyl amine as base. The results are given in
Table 1. The TON value are high (upto ꢁ95,000) showing the prom-
ise of both 1 and 2 as catalyst for Heck coupling. However, the TON
values when Pd-complex of (Se, C, Se) pincer ligand is used, are
upto 1,10,000. The performance of 1 and 2 both is much superior
than that of palladium salicylaldehyde thiosemicarbazone com-
plex, which shows TON values upto 43,000 only [61]. For aryl chlo-
rides 1 mol% of phosphine based palladacycle is needed for high
yield of the reaction [64]. The 1 and 2 for catalyzing Heck reaction
are as efficient as Pd-complexes of (Se, N, Se) pincer ligand re-
ported recently [66] (TON upto 97,000).
4
5
8.8 ꢂ 104 (88) 9.1 ꢂ 104 (91)
9.2 ꢂ 104 (92) 9.4 ꢂ 104 (94)
OH
O
their selenium analogues. The TON values are <10,000 when
Pd-complex of a selenated Schiff bases is used as catalyst for
Suzuki–Miyaura coupling. Phosphine ligand based Pd-complexes
are suitable for Suzuki–Miyaura coupling of aryl chlorides but
the requirements of a co-catalyst and high mol% of catalyst are
stringent [64–68]. In the course of Suzuki–Miyaura coupling
reaction there was a black deposit formation (Pd(0)), indicating
that the mechanism of catalysis by 1 and 2 is probably Pd(II)/
Pd(0) one.
Ar
Complex 1 or 2
+
Br
Ar
n-butylamine
p-xylene, N2
COOMe
COOMe
ð1Þ
Suzuki–Miyaura reaction, is also among the most important
palladium-catalyzed cross-coupling reactions of both academic
and industrial interest [62–69]. In view of air and moisture sensi-
tivity of complexes of phosphorus ligands there is an interest in
phosphine-free ligands for the Suzuki–Miyaura reaction. The
complexes 1 and 2 have been explored for Suzuki–Miyaura
reaction (Eq. (2)). The results given in Table 2, indicate that both
the complexes are promising. The results given in Tables 1 and 2
also indicate that Pd(II)-telluroether complexes are as efficient as
Complex 1 or 2
+
Br
B(OH)2
Ar
R
toluene, K2CO3
R = H, Me, CN, CHO, NO2
ð2Þ

D. Das et al. / Journal of Organometallic Chemistry 695 (2010) 955–962
961
The catalytic oxidation (Eq. (3)) in the presence of complexes 3 and
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